Endoprosthesis of the knee and/or other joints

ABSTRACT

The principle of this endoprosthesis of the knee can also be used in other joints, that require a bearing during movement of the parts, with the aim of reducing wear. This endoprosthesis has improved self-lubrication mechanisms, the ability to filter the particles from the debris produced by the moving parts, and a new viscoelastic behavior under loading which reduce the transmitted forces. This has been achieved with the use of compressible materials ( 13 ) and mechanisms [for example between the fixed bearing ( 25 ) and the tibial component ( 24 )], allowing the endoprosthesis to have compressibility under loading, which allows it also to receive or create chambers ( 14 ) with an exit ( 26 ) to the surface articulating with the femoral condyles ( 15  ). These chambers ( 14 ) can be compressed ( 13   a ) and decompressed ( 13   b ), accumulate and spurt out ( 16 ) synovial fluid, from and to the articulating surfaces. The movement of the synovial fluid and gases from and to ( 16 - 19 ) the exit ( 26 ) openings creates viscoelasticity, and improves the lubrication of the moving parts. Simultaneously, permeable filter ( 21 ) materials interpolate to the synovial fluid flow ( 16 - 19 ) trapping the debris.

The invention concerns a endoprosthesis of the knee and/or other joints,where the implant or platform, mobile or fixed, of polyethylene or othermaterial is used.

The standard endoprosthesis of a knee joint consists of three parts,

-   -   1. the femoral component,    -   2. the tibial component    -   3. & an implant made of polyethylene or other material, which        can be either fixed on to the tibial component, or mobile in        relation to the tibial component.

Subsequently, the description, when the implant platform is fixed on thetibial component will be called “the fixed bearing”, and when theimplant platform moves on the tibial component will be called “mobilebearing”. The superior surface of the fixed bearing or mobile bearingarticulates with the metal or other material femoral component, and theinferior surface with the tibial component. It is known that thephysiological articular cartilage of the joints generally (andparticularly the knee joint which receives extensive forces) isprotected from wear and injuries by the following three properties:

-   -   1. it has the ability to absorb forces and compressive loads        that are applied in an elastic and viscoelastic way.    -   2. the ability of the articular cartilage to adapt its surfaces        by conforming itself after a period of static loading.    -   3. The continuous lubrication of the synovial fluid which is in        the joint space and in the articular cartilage.

There are 4 theories how this lubrication occurs: boundary lubrication,hydrodynamic lubrication, weeping lubrication, and elastohydrodynamiclubrication. (Journal of Orthopedic and Sports Physical Therapy,0196-611/82/0304-0186 (volume 13, number 4).

The viscoelastic absorption of the forces are exerted on to thearticular cartilage and are due to combined factors.

-   -   A—progressive entry and exit of the synovial fluid within the        substance of the articular cartilage.    -   B—the elastic absorption of the forces from the collagenous        fibres, the proteoglycan network, and solid fibres of the        articular cartilage.

This invention refers to an endoprosthesis for the knee and/or otherjoints that use a fixed or mobile bearing, and components covering thearticular surface of the bones.

This invention is characterized by viscoelastic behavior duringcompression (as in loading) and during decompression (as in unloading),by integral chambers in the components that consist of, chambers whichcommunicate with the joint space through small openings or holes. It isalso characterized by the possibility of the chambers ability toaspirate and accumulate synovial fluid and gases during unloading andextrude fluid and gases to the joint space during loading. Anothercharacteristic is that it has materials which are permeable to thesynovial fluid. These materials interpolate to the synovial fluid flowand filter it from the wear debris which circulates in the synovialfluid of the endoprosthesis.

Until now the fixed or mobile bearings that are being used in total kneeendoprosthesis, or other joint endoprostheses, have mainly been madefrom ultra high molecular weight polyethylene or other material such asceramic. The manufactured bearings and their connection with the tibialcomponent have neither the ability nor the function to make use of thesynovial fluid for an effective lubrication. They do not have theability to filter the debris particles, nor to progressively absorb theforces that are exerted during knee movement.

Another element is that the bearings either mobile or fixed to thetibial component cannot adapt their shape and position in relation tothe anteroposterior and transverse axis, which adaptation is relevant tothe direction of load received. As a result of this, there is increasedwear of the bearings and moving surfaces especially of the polyethylene,because the surfaces move with increased frictional forces that causescraping, delamination, pitting, and fatigue.

The bearings do not have the above-named properties and the surfaces areless conforming, and therefore there is unequal distribution of load.These features contribute significantly to the potential failure of theendoprosthesis, instead of the expected successful result from such anoperation.

In October 2001, a new prosthesis was described as a patent applicationwith an elastic material between the inferior and superior parts of itsmobile bearing body, (pat.GB2348373)—another description (GB2348373) isof a tibial prosthesis component with an elastic material between theupper part of the metal tibial component that comes into contact withthe mobile bearing and the metallic undersurface sitting on the tibialbone. Neither of these applications offer any potential for thelubrication of the surfaces and therefore no reduction in the damagefrom wear, such as scraping and delamination etc. Neither do they havethe ability to filter the debris, nor a progressive viscoelasticabsorption of the forces or adaptation, and specifically the descriptionof the mobile bearing with only one compressible material between theupper and lower part of its body may be unsafe and be difficult for thebearing to have manufacturing bonding.

In contrast to the above, this invention aims to produce anendoprosthesis for the knee and/or other joints with fixed or mobilebearing (made from polyethylene or other materials that arebiocompatible) and that can adapt to the direction and type of forcesreceived, and thus progressively absorb by viscoelastic behavior andredistribute the load forces, with a possibly improved range of jointmovement.

Finally, to make use of synovial fluid for better lubrication of theendoprosthesis, and to have the ability to filter the wear debris whichis produced by frictional forces of the materials.

In order for this invention to be achieved, compressible, resilient,adaptable, elastic materials, some of which will allow fluid and gasesto penetrate, or a mechanical device or devices with spring actionproperties, or combination of these, will be inserted inbetween themobile or fixed bearing body or inbetween the superior surface of themetal tibial component and the inferior surface of the bearing, orinbetween the tibial component body. In the case of the mobile bearing,this can only be achieved by using a mechanical device with springaction properties inbetween the superior part and inferior part of themobile bearing. These inserted materials or mechanical devices arebiocompatible, and their form and manufactured shape creates integralchambers, or are made to receive independent chambers, that communicatewith the joint space through small holes or small openings on the fixedor mobile bearing body, the interposed material, or the tibialcomponent. These chambers function as pumps through which the synovialfluid circulates in and out. The communicating chambers enclosebiocompatible materials which in a rightful position allow synovialfluid and gases to penetrate, and as a result of this they filter thewear debris, polyethylene or metal, which is within the joint.

The invention will be described in relation to numbered designs in theform of a few examples, to avoid mentioning too many.

Design 1 shows in an illustrated form the function of lubrication andviscoelastic compression during loading.

Design 2 shows in an illustrated form the function of lubrication andviscoelastic decompression during unloading.

Design 3 shows in an illustrated form the function of lubrication andfiltering during loading.

Design 4 shows a ground plan of an example in use according to theinvention

Design 5 shows a section of level II-II of Design 4.

Design 6 shows a perspective form of another way of using of theinvention in part form.

Design 7 shows a ground plan of design 6, of the way of use of theinvention as Design 6.

Design 8 shows a section at the level of III-III of the Design 7.

Design 9 shows a section that describes another type of use of theinvention.

Design 10 shows a section of another example of use according to theinvention.

Design 11 shows a perspective view of an example of use, based on theinvention using a mobile bearing.

Design 12 shows a section at the level of IV of Design 11 in relation tothe mobile bearing (not in relation to the tibial component).

DESCRIPTION IN DETAIL OF THE ABOVE DESIGNS

Designs 1,2,3 describe the basic principle and function of thisinvention and demonstrate the cycle of loading and unloading (forexample during walking) according to the invention. The three designsshow that a part of the fixed bearing (25) that articulates conforminglywith the femoral component (15), the tibial component (24), and acompressible component (13) (according to the previous descriptions),which is inbetween the fixed bearing (25) and the tibial component (24).This fixed bearing (25), has hole (26), and this hole opens on thesuperior surface of the fixed bearing (25), where the femoral condyle(15) articulates with the fixed bearing (25), (as is shown in thesediagrams, for descriptive reasons, only in relation to one condyleinstead of two). The inferior opening of the hole (26) (distally) endsin a shaped chamber (14), which is formed of the wall of the superiorsurface of the tibial component (24), and the inferior surface of thefixed bearing (25), and circumferentially from the wall of thecompressible material (13), of which the shape underneath the bottom ofthe hole (26), forms the chamber (14).

During the period when the endoprosthesis is not in use (for examplesitting) the synovial fluid progressively collects in the concave partof the fixed bearing (25), and from there into the hole (26), to thechamber (14). During loading of the endoprosthesis (stance phase andwalking), the vertical loading that is exerted by the femoral component(15), to the fixed bearing (25) is transmitted to the compressiblecomponent (13), the thickness of each, is reduced (13 a) and thedistance between the inferior surface of the fixed bearing (25), and thesuperior surface of the tibial component (24), becomes smaller (13 a),and therefore there is a reduction in size and capacity of the chamber(14). As a result of the reduction in size and capacity of the chamber(14), the synovial fluid and gases which are collected in the chamber(14) are forced because of increased pressure to exit (16), through thehole (26), in the superior surface of the fixed bearing (25), of thepart that articulates with the femoral component (15). The force andpressure of the synovial fluid spurts and exits (16) of the hole (26),or the chamber (14), is related to the amount of loading exerted uponthe endoprosthesis. The presence of synovial fluid during loading, withsome pressure and in a certain amount of it, at the fixed bearing (25)part which has better contact with the moving femoral component (15),reduces the frictional forces and wear between the contact surfaces offixed bearing (25) and femoral component (15), because an amount of thesynovial fluid interpolates (17) between the contact surfaces of thefemoral component (15) and the fixed bearing (25), and the reduction offriction is mainly due to hydrostatic and hydrodynamic lubricationmechanism, and in some part of the lubrication with the squeeze-filmmechanism (Basic Biomechanics of the Skeletal System, Victor H Frankel,Margareta Nordin, Lea & Febiger, Phil. USA.)

The synovial fluid and the gases which are accumulated in the chamber(14), need time to exit (16) from the hole (26), and this depends on thesize of the hole (26), if it is covered by the femoral component (15),the viscosity of the synovial fluid and the amount of loading. Thereforethe compressibility of the elastic component (13), and all this unit,depends also on the speed of the exit (16) of the synovial fluid andgases from the chamber (14), and this unit reacts not only in relationto the amount of loading but also to the time it receives the load. Thisreaction to the load is called viscoelasticity, and makes theendoprosthesis behave and absorb the forces in a similar way to a normalcartilaginous joint. It is this property of the invention that gives itthe ability to receive an increase in the loading of the endoprosthesis,because it can absorb gradually and smoothly the forces by thecompressible component (13) and also by the energy that is absorbedduring exit (16)-entry (19) of the synovial fluid and gases from chamber(14). The re-entry (19) of synovial fluid and gases in the chamber (14),occurs during the phase of unloading of the endoprosthesis, design 2,and enlarges as the compressible component (13) resumes its previoussize (13 b) and the chamber (14) increase its size and capacity. At thatmoment the reduced pressure in chamber (14), in relation to thearticular space, forces the synovial fluid and gases to re-enter (19)the chamber (14). The synovial fluid is directed to hole (26) because ofthe gravity, particularly as the superior opening of hole (26) is at thedeepest point of the superior surface of the fixed bearing (25), thepoint of the largest contact surface area with femoral component (15).During the re-entry phase (19) of the synovial fluid and gases to thechamber (14), all the unit does not return immediately to the neutralposition after unloading, because the re-entry phase takes some time forthis, so the endoprosthesis keeps the viscoelastic behavior duringunloading. Once they collect again in chamber (14) during the nextloading phase, the cycle that has previously been described above startsagain. During this cycle of compression (13 a) and decompression (13 b)of the fixed bearing (25) in relation to the tibial component (24), andexit (16)-entry (19) of the synovial fluid, interpolate in its path,design 3, a biocompatible, elastic, hydrophilic, or not hydrophilicmaterial (21) that is permeable (22),(23) by the synovial fluid, whichis resilient to pollution from stagnant proteins and/or other biologicalcomponents of the synovial fluid, and is at the same time able towithhold debris, particles of metal and polyethylene or other materialsproduced by the friction of the parts of the endoprosthesis.

This invention therefore has the ability and the capability to filterand retain debris, reduce their quantity, and thus increase the lifespanof the endoprosthesis by avoiding osteolysis. The synovial fluid canpass (22),(23) entirely or as substrate through the filter. Theappropriate materials (21) for filters can have as constituent parts,silicone, rubber, hydroxyl-ethyl-methacrylate(hema), thepolyvinylpirrolidone (PVP), methylmethacrylate (A), or other materialsknown by commercial names such as ES70, manufactured by Essilor, orBalafilcon by Bausch and Lomp. Some of the above materials have elasticproperties, others only hydrophilic, some elastic and hydrophilic, someare neither elastic nor hydrophilic but are only permeable to thesynovial fluid, and their combined use can provide a material (21)suitable for filters. These named materials are not the only ones thatcan be used. There are several others that are suitable. As well as someforms shown in designs 6,7,8, the compressible material functions alsoas a filter, and the physical properties of the material in this formcan be characterized by its ability to be compressible material andfilter together, as compared to other materials that can only be used asfilters. Following a detailed explanation in designs 4 and 5, an exampleis given of the way that this invention is used, where the fixed bearing(25) and the tibial component (24), use elastic and compressiblematerial (13) placed inbetween them transversely and peripherally. Thismaterial (13) can be biocompatible using silicone, silastic or a form ofrubber or other material. The peripheral compressible material (13),when in place creates a closed chamber (14) where its superior surfaceis the inferior surface of the fixed bearing (25), its inferior surfaceis the superior surface of the tibial component (24), while peripherallyit is composed of compressible material (13). At the central area of thechamber (14) is positioned a filter material (21) which has thecharacteristic properties similar to those described in design 3 asfilter material (21) properties. The areas of chamber (14) that arebeneath the level of the contact surfaces of the fixed bearing (25)articulates with the femoral component (not shown), which remains empty,whilst in these areas holes (26) go through the body of the fixedbearing (25), bringing into contact the joint space and the superiorsurface of the fixed bearing (25), with the chamber (14). Another hole(27), transverses the fixed bearing (25), at a central point bringing incontact the area of the chamber (14) which contains the filter (21) withthe joint space. A ring (28) with spring action properties made frombiocompatible material stabilizes the fixed bearing (25) on the tibialcomponent (24), allowing the fixed bearing (25) when it receives loads,to compress the elastic compressible material (13), and move nearer tothe tibial component (24), and when unloading it returns to its initialposition moving away from the tibial component (24), not being able todislocate the fixed bearing (25) from the tibial component (24). Thering (28), may not cover all of the periphery of the tibial component(24), leaving a small space (28A), and having the ability to constrict,bringing its edges closer. Because of the constriction ability of thering (28), the fixed bearing (25) can be coupled and decoupled andremains stable on the tibial component (24), whilst at the same time iscompressible in relation to the tibial component (24). The shape andmoulding of the ring (28), serves the above needs. The way that thistype of invention works follows the descriptions of designs 1, 2, 3. Thesynovial fluid in this type of use the invention passes partiallythrough the filter (21), and all the unit behaves both elastically andviscoelastically.

Designs 6,7, and 8, show another way of using the invention where thebasic components remain the same as those in designs 4 and 5.

Chamber (14) is made out of the inferior part of the fixed bearing (25)the superior surface of the tibial component (24), and peripherally bythe ring (28) of the stabilization-connection. In between the tibialcomponent (24), and the fixed bearing (25), there is an elastic material(21), which is biocompatible and compressible, permeable to the synovialfluid, with all the characteristics described in design 3 as a filteringmaterial (21). The holes (26), which communicate the chamber (14) withthe joint space, have their superior opening on the superior surface ofthe fixed bearing (25) at the contact area with the femoral component(design not shown) and their inferior opening in direct contact with thecompressible material (21).

This use of the invention follows the function described in designs1,2,3, but it has the characteristic that most of the synovial fluidthat enters (19) and then exits (16) during use, passes through the bodyof compressible material (21), mainly during the entry (19) to chamber(14) but also during exit (16). A small quantity enters the chamber (14)through the specially formed ring (28), as well as the small space(28A), and from the declivity of the circumferential margin (24A) of thetibial component. This creates a better filtering of debris. The wholeunit has viscoelastic behavior considering the way that theendoprosthesis absorbs the forces exerted.

Designs 9,10, describe another way of use according to the inventionwhere the basic components remain the same as designs 4,5,6,7,8, andwith more analytical details , in design 9 the intermediate material(13) inbetween the fixed bearing (25) and the tibial component (24) is abiocompatible, compressible, elastic, non hydrophilic material (13) suchas silicone, silastic, rubber or other material, which covers almost allthe inferior surface of the fixed bearing (25) as shown in design 9, andas a result this endoprosthesis behaves as viscoelastic, but the elasticproperty is greater than the other designs described. In design 9, wehave two as shown (with the possibility of additional) autonomouschambers (14) which partially take over space also within the interiorpart of the body of the fixed bearing (25) and within the body ofcompressible material (13). These chambers (14) communicate with thejoint space with vertical holes (26) which traverse the body of thefixed bearing (25) in the areas of contact with the femoral condyles(not shown). In their superior part there is a noncompressible, nonelastic, permeable by synovial fluid filter (21) with the propertiessimilar to those described in design 3, as filter material (21)properties.

A spiral form (29) holds the filter (21) in the top part of chamber (14)whilst simultaneously permitting the passage of synovial fluid throughthe spiral form (29), and through the filter material (21). The bottompart of chamber (14) remains empty and the filter (21) does not comeinto contact with the tibial component (24) even during maximumcompressive activity. The spiral form (29) (spring like) can be made outof any biocompatible material is capable of such a function.Functionally this way of using this invention is different, becausefilter (21) can be used without being compressible, and the small sizeof the chambers (14) and the specific placement that they have, createconditions of increased exit pressure for synovial fluid and improvedlubrication on the basis of hydrostatic mechanism.

In design 10 there is a way of using the invention which behavesviscoelastically, having compressible material (13) permeable only togases, having in its substance microchambers that work as the chambers(14) previously described, allowing this compressible material (13) tohave the possibility to aspirate and push out gases during decompressionand compression of the endoprosthesis through the hole (27A) andcircumferential at the point of contact between the ring (28) and thefixed bearing (25). In this design the microchambers are not shown. Alsoin design 10 the compressible material (13) could be totally elastic ifwhat is required is only elastic absorption of forces.

Designs 11,12 show, according to the invention, a way of using anendoprosthesis with a mobile bearing. The mobile bearing according tothe designs consists of a superior part (30) an inferior part (31) andan intermediate part made out of a compressible mechanism (32) (forexample a spring). These three parts are joined to each other bymechanical means, or biocompatible adhesive or by a combination ofthese, to a unified functioning mobile bearing that can move, glide, androtate in all directions on the tibial component (24). These three parts(30),(31),(32) of the mobile bearing which are joined together, howevervarying the manufacturing characteristics (33) may be or havearticulating surfaces (33) conforming or nonconforming, and usingbollards or stops to prevent dislocation, allows it to work as acomplete entity as far as compressibility of the mobile bearing isconcerned and moving on the tibial component (24) as with, all othernoncompressible mobile bearings already in use, but which lack thecompressible element described.

The superior part (30) of the mobile bearing has vertical holes (26)that traverse its body and go through the superior part of compressiblemechanism (32) into the chambers (14) placed in the empty spaces of thecompressible mechanism (32). Also other holes (34) which have as asuperior opening the superior surface of the superior part (30) of themobile bearing, and inferior opening the inferior surface of theinferior part (31) of the mobile bearing, traversing through theintermediate compressible mechanism(32), leaving the synovial fluid topass through to the contact surface area of the tibial component (24),with the inferior surface of the mobile bearing improving also thelubrication at this level. The ability of the mobile bearing to becompressed and also to receive or to create chambers (14) whichcommunicate with its superior part (30) where the femoral component (not shown) articulates, allowing the mobile bearing to function asdescribed with this invention in a similar way as the endoprostheseswith a fixed bearing (25) described previously.

It also could have empty spaces instead of chambers (14), with filtermaterial (21) as described in the designs 6,7,8 or any other combinationbased on the ideas and the purpose of this invention. Also in relationto the suitable materials , the fixed bearing as well as the superiorand inferior part of the mobile bearing, can be made out of ultra highmolecular weight polyethylene, or from any biocompatible materialappropriate for this use, such as carbon fibres, cobalt chromium alloy,alumina ceramic or zirconium, or a combination of them, or any othermaterial that will give increased resilience with less thickness andtherefore wider and more effective use of the invention. The use of theabove mentioned materials or a combination can be used and in the caseof the tibial component, or generally the components covering thearticular surface of the bones, (which are usually made out of cobaltchromium alloy), and also for the compressible mechanisms (e.g. springor ring) that can be used in the mobile bearing or inbetween the fixedbearing and the tibial component or as tibial component and fixedbearing connection ring. Specifically for the construction of a springmechanism, any biocompatible metal or plastic or combination of thesethat can give resistance to repeated distortions and elastic properties.The invention can also be widely used when applied to the alreadyavailable endoprostheses in clinical use, by some changes made in theshape and moulding of the inferior part of the fixed bearing which incombination with construction of an appropriate ring or mechanism willkeep and stabilize the fixed bearing in place upon the tibial component,for each type of endoprostheses, allowing compression and decompressionof the fixed bearing in relation to the tibial component, and in generalthe complete function of the invention without dislocation of the fixedbearing from the tibial component. This can be done without changes orwith some very small changes being made to those already available inclinical use tibial components for knee endoprosthesis, reducing thecost of manufacturing. The same applies (as described in designs 11,12.)and in the case of the mobile bearing but also for all types ofendoprostheses that are described for other joints (other than knee) andwhich have in their constituent parts, components covering the articularsurface of the bones and fixed bearings or mobile bearings for betterarticulation.

Advangages:

The advantages of an endoprosthesis that contains a fixed bearing or amobile bearing such as described above according to the invention aremultiple and are related to the way it is produced. If simply the fixedbearing and the tibial component have inbetween them a compressibleelastic material (design 10), or a mechanism specially in the case of amobile bearing, then the fixed bearing and by extension theendoprosthesis has the ability to absorb and redistribute the forcesthat are exerted during use, with better and more homogeneousdistribution upon the tibial and femoral component. In addition to theabove benefits, full use of them is made when the ability of the fixedbearing, or of the mobile bearing, to be compressed and decompressed byitself or in relation to the tibial component is incorporated withmaterials and other forms that have been described for the function ofself-lubrication, filtering, viscoelastic absorption of the forces andadaptation. The adaptation of the fixed bearing and the mobile bearingto the loads ensures a more conforming contact surface area with thefemoral component. The improved lubrication that occurs on the contactsurface area reduces friction and concurrently the wear of the mobileparts. Reduced wear means a longer lifespan of the endoprosthesis andreduction in wear debris in the joint space. The reduction of the weardebris is helped by the function of the filtering significantly reducesthe probability of osteolysis, and in general the toxic effect thatthese particles which might have upon the joint and the body. Theprogressive absorption means that if after the exertion of a verticalload upon the joint another vertical load added to the first one, theendoproshesis still has the ability to absorb the first and allsubsequent loads successfully as the compression range continues. Forexample on climbing or coming down slowly a step the gradual absorptionallows the endoprosthesis to distribute and absorb the forces that areplaced upon it through the range of movement rather than just theinitial phase. The adaptability of the fixed bearing or mobile bearingaccording to the invention adds another significant advantage, forexample when the fixed bearing receives forces at a specific point andfor a prolonged period of time distributes and disperses the synovialfluid into the compressible material (e.g. designs 6,7,8) depending onto the direction of the forces that it receives. The adaptability allowsthe fixed bearing to change position in relation to the tibialcomponent, a change in position that is not lost immediately after theseforces or loads stop. If the same loading is repeated again immediatelyafter the previous, the fixed bearing keeps the adapted positionimproving the mobility. This can also occur during deep sitting wherethe fixed bearing will acquire a posterior inclination, improving therange of movement of the endoprosthesis in flexion, improving itsstability, and contributes a improved contact area with the femoralcomponent. In fast walking where the knee hyperextends a viscoelasticadaptation of the fixed bearing in anterior inclination improves theextension of the joint and as result the gait. In fast walking the abovedescribed occur in the same direction in shorter periods of time and theviscoelastic behavior does not allow the fixed bearing to lose itsanterior inclination. All these descriptions also apply to the mobilebearing.

The gradual absorption of the load, prolongs the time that synovialfluid exits during self-lubrication and maintains the lubricationmechanism, even in slow motion with greater loads (e.g. climbingstairs).

In total, the application of the invention in an endoprosthesis, allowsit to receive larger loads, with less wear. An endoprosthesis thatsimulates a natural joint regarding function, an endoprosthesis that canbe used in younger and more active patients, tolerating the increasedactivities, and prolonging its life expectancy. The possibilities ofadaptation that it offers, make it easier for surgical application. Inunicompartimental endoprosthesis, which is more sensitive to the forcesapplied than total knee endoprosthesis and achieves a more normalfunction because of more synovial fluid available, the use of thisinvention as a unicompartimental endoprosthesis is strongly recommendedbecause of its ability to make more use of the synovial fluid. Thedescriptions of this invention and its use were only given in the formof examples in order to explain the concept, and its application inclinical use. Many changes and variations can be mode or added followingthe general principles of this invention. For example, the holes for thepassage of the synovial fluid can be one or several, or one-way valvescan be used, so that the synovial flow, is directed by certain holesonly (e.g. Only through the filters), or the chambers as many asnecessary can be an integral part of the bearing body or the tibialcomponent substance. For this reason, this application has the intentionof covering any variations, use or adaptation using the generalprinciples and concept of this invention, and which fall within thelimits of the appended claims.

1. Endoprosthesis of the knee joint with possibilities of viscoelasticabsorption of forces, improved self-lubrication mechanisms and filteringof wear debris, which consists of a fixed bearing (25) that is heldfirmly with a tibial component (24), having an articular superiorbearing surface for engagement with a femoral component (15), and ischaracterized by the fact that the inferior surface of the said fixedbearing (25) does not abut against the superior surface of the saidtibial component (24), but inbetween them there is an interspace with acompressible mechanism (32) placed in a tranverse level, and thestabilization of the said fixed bearing (25) on the said tibialcomponent (24) occurs with a circumferential connecting ring (28) orother mechanical means in such a way that it allows the fixed bearing(25) the possibility when it receives load or weight to compress thecompressible mechanism (32), and the body of the fixed bearing (25)moves approaching the tibial component (24) making their interspacesmaller (13 a), and during decompression the body of the fixed bearing(25) moves to the opposite direction increasing (13 b) the interspacebetween the said fixed bearing (25) and the said tibial component (24),and this movement of compression (13 a) and decompression (13 b) of thefixed bearing (25) to the tibial component (24) during use occurs withno possibility for decoupling or dislocation, of the said fixed bearing(25) from the said tibial component (24), and which compressiblemechanisms (32) with their position, shape, and manufacturing, createsin combination with the inferior surface of the fixed bearing (25), withthe tibial component (24), and with the connecting mechanical means andring (28), one or more chambers (14), or receives one or more autonomousshaped molded chambers (14), which can change their size and capacity,said chambers (14) which communicate with the joint space through holes(26), and/or small openings (28A), said holes (26) which traversethrough the fixed bearing (25) body, and their superior opening is atthe superior surface of the fixed bearing (25), at areas where thesynovial fluid is collected, the moving parts transmit the largest load,and where there is better conformity and articulation with the femoralcomponent (15), said chambers (14) which aspirate and accumulate thesynovial fluid and gases during unloading of the endoprosthesis, andexit (16) the fluid and gases to the joint space during loading, addinghydrostatic self-lubricated mechanism, and in this synovial fluid flow(16)-(19) of entry (16) and exit (19), from and to the chambers,interpolates appropriate materials (21) which are permeable (22),(23) tothe synovial fluid, and filter the synovial fluid trapping the weardebris produced by the friction of the parts of the endoprosthesis,which are in the synovial fluid.
 2. Endoprothesis of claim 1, which ischaracterized by the fact that inbetween the fixed bearing (25) and thetibial component (24), in the interspace, there are compressiblematerials (13) or a combination of compressible materials (13) andmechanisms (32), which said compressible material (13) and saidcompressible mechanisms (32) when placed, shaped, and manufactured, cancreate in combination with the inferior surface of the fixed bearing(25), with the tibial component (24) and with the connecting mechanicalmeans or ring (28), one or more chambers (14), or receives one or moreautonomous chambers related to the molding, and said compressiblematerials (13) which could be elastic with or without hydrophilicproperties, permeable (22)(23) by synovial fluid, or to consist solelyof elastic parts such as silicone or rubber non-permeable by synovialfluid, with parts permeable (22)(23) by synovial fluid, or to be elasticpermeable by gases, or to be solely elastic parts non-permeable by gaseswith parts permeable by gases, said compressible materials (13) whenpermeable by synovial fluid function simultaneously as filter material(21) for trapping the wear debris which is in the synovial fluid. 3.Endoprothesis of claim 1, which has inbetween the fixed bearing (25) andthe tibial component (24) in their interspace a compressible material(13), and is characterized by the fact that the said compressiblematerial (13) has in its substance microchambers into which gases enter(16) during unloading and gases exit (19) during loading. 4.Endoprosthesis of the knee of claim 1 which is characterized by the factthat inbetween the fixed bearing (25) and the tibial component (24) intheir interspace there is only compressible material (13) which issolely elastic.
 5. Endoprosthesis of the knee of claim 1 characterizedby the fact that instead of fixed bearing (25), a mobile bearing isused.
 6. Endoprosthesis of the knee of claim 1, claim 3, and claim 5,which is characterized by the fact that it has compressible mechanism(32) inbetween and transversely through the body of the mobile bearingin its cross-section, or inbetween and transversely of the body of thefixed bearing (25) in its cross-section, or inbetween and transverselyof the body of the tibial component (24) in its cross-section, where thesuperior part (30) of the body of said mobile bearing, or of said fixedbearing (25), or of said tibial component (24), the said inclusivecompressible mechanism (32), and the inferior part (31) of the body ofsaid mobile bearing, or of said fixed bearing (25), or of said tibialcomponent (24) corresponding parts, are joined to each other to aunified compressible structure, and this unified compressible structurehas one or more holes (26) which pass through its body to connect thechambers (14) with the joint space, said unified compressible structurewhich has the manufacturing characteristics (33), the articulatingsurfaces (33) or stops, in such a way that allows the unifiedcompressible mobile bearing, or the unified compressible fixed bearing(25), or the unified compressible tibial component (24) to work andfunction as all other noncompressible mobile bearings, ornoncompressible fixed bearings (25), or non compressible tibialcomponent (24) already in use, and in addition for the compressiblemobile bearing to move on the tibial component (24) as with all othernoncompressible mobile bearings in use.
 7. Enthoprosthesis of the kneejoint of claim 1, claim 2, claim 5, and claim 6, which is characterizedby the fact that the compressible mechanisms (32)(29) and connectingring (28), have spring action properties and could be made from anymetal, plastic, ceramic, alloy, or any combination of the above, orother material suitable and biocompatible for this use. 8.Enthoprosthesis of the knee joint of claim 1, claim 2, claim 3, claim 5,and claim 6, which is characterized by the fact that enclose one or morechambers (14) said chambers (14) which can adapt to different size andcapacity, said chambers (14) which can be autonomous or can be anintegral part of the knee components, said chambers (14) which may ormay not have a filter (21) material inside, said chambers (14) which canbe placed into the body of the fixed bearing (25) or the mobile bearing,said chambers (14) which can be placed into the body of the compressiblematerial (13) and mechanism (32), said chambers (14) which can be placedinto the body of the tibial component (24) or the component which coversthe articular surface of the bone, said chambers (14) which communicatewith the joint space through holes (26) and small openings (28A), andtheir capacity and size increase during unloading of the knee joint, anddecrease during loading of the knee joint.
 9. Enthoprosthesis of theknee joint as claimed in claim 1, claim 2, claim 3, claim 5, claim 6,and claim 8, in which the pressure into the chambers (14) can change byincreasing or decreasing during loading and unloading of the joint, saidpressure into the chambers (14) which increases or decreases in relationto the joint space pressure, and forces the synovial fluid and gases topass through the holes (26) and small openings (28A) from the jointspace to the chambers (14), and from the chambers (14) to the jointspace, said passage of the synovial fluid and gases through the holes(26) and small openings (28A) create a viscoelastic behaviour duringloading and unloading of the joint.
 10. Enthoprosthesis of the kneejoint as claimed in claim 1, claim 2, claim 5, claim 6, claim 8, andclaim 9, in which the trapping of the wear debris, and filtering of thesynovial fluid occur in a mechanical way from the filter (21) materialswhich interpolate to the synovial fluid flow (16)-(19), said synovialfluid flow which created by the movement of the fluid from the chambers(14) to the joint space and from the joint space to the chambers (14),said filter (21) materials which are elastic or not elastic,biocompatible, hydrophilic or not hydrophilic, permeable by the synovialfluid, resilient to biological components of the joint fluid, saidfilter (21) materials could have as constituent parts silicone, rubber,hydroxyethylmethacrylate(hema), polyvinylprirrolidone(PVP),methylmethacrylate (MMA), or any other appropriate materials withsuitable mechanical properties, and can be used for filtering thesynovial fluid from wear debris.
 11. Endoprosthesis of the knee joint asclaimed in claim 1, claim 2, claim 5, claim 6, claim 8, claim 9, andclaim 10, in which the superior openings of some or all of the holes(26) of the bearings, are at the concave superior surface of the fixed(25) or mobile bearing, where the femoral component (15) has betterarticulation, transmits larger loads, and more synovial fluid surfaces,said superior openings of the holes (26) from which spurt out (19) withpressure the synovial fluid augmenting the already normal lubricationmechanisms of the joint, and creating hydrostatic lubricationmechanisms.
 12. Endoprosthesis of the knee joint as claimed in claim 5,claim 6, and claim 11, which is characterized by the fact that it has amobile bearing which has one or more holes (34) which traversevertically the body of the mobile bearing, said holes (34) which have asa superior opening the superior surface of the mobile bearing and as ainferior opening the inferior surface of the mobile bearing, allowingthe synovial fluid to pass through, into the openings and holes (34)from the superior surface of the mobile bearing to the contact surfacearea of the tibial component (24) with the inferior surface of themobile bearing.
 13. Endoprosthesis of the knee joint as claimed in anyone of the preceding claims for unicompartmental endoprosthesis. 14.Endoprosthesis as claimed in claim 1, claim 3, claim 7, claim 8, claim9, claim 10, and claim 11, for hip joint, and for ankle joint. 15.Endoprosthesis of the knee joint as claimed in any one of the precedingclaims in which their constituent parts are biocompatible, and can bemanufactured from any plastic, metal, ceramic, alloy or otherappropriate materials.